This invention relates to intravascular (I.V.) catheters and, in particular, to I.V. catheter assemblies which cover the needle point after use to prevent accidental injury from used needles.
Intravenous catheters for the infusion of fluids into the peripheral veins of a patient are one of the most common devices used in I.V. therapy I.V. catheters may be produced in two general forms: through-the-needle catheters, in which a catheter is threaded through the needle cannula and into the vein of a patient, and over-the-needle catheters, in which the needle and concentric outer catheter are inserted into the vein and the needle is withdrawn through the emplaced catheter.
A typical over-the-needle I.V. catheter assembly requires the user to remove and then dispose of a contaminated needle after the needle tip and catheter are properly located in a blood vessel of a patient Once the needle is withdrawn from the catheter, the user's immediate priorities are infusion set connection and site preparation, including the taping of the catheter to the patient. Because of the urgency of these procedures, the needle is normally just dropped conveniently nearby and then retrieved later. Since the needle at this time is exposed and located close to where the user is completing work with the catheter, accidental self-inflicted needle injuries are not uncommon. For reasons of the desirability of protecting the user from exposure to blood borne disease such as hepatitis and AIDS, there is an increasing need to protect the user from accidental needle injury.
A catheter design which is directed toward this need is shown in U.S. Pat. No. 4,762,516. The catheter shown in this application includes an elongate body which houses a sliding needle guard. In use, the needle with its surrounding catheter tube is inserted through the skin of a patient until the tip of the needle is located in a blood vessel, a position detected by a small flow of blood through the needle and into the flash chamber of the catheter The user then advances a tab on the top of the needle guard to simultaneously thread the catheter tube into the blood vessel and begin the retraction of the needle from the catheter tube. As the needle is withdrawn from the emplaced catheter, the advance of the tab slides the needle guard out of the housing and along the needle, until the distal end of the guard covers the needle tip and the proximal end of the guard locks in the elongate body. The needle and guard may then be set aside with the needle tip fully protected.
While the arrangement described in this patent application can provide full protection against accidental needle injury, it would be desirable to provide such a catheter in a smaller, smoothly operating configuration which can be readily manipulated by small hands. In this invention, a catheter assembly with needle guard is provided with a semi-tubular needle housing that is open on the upper surface. Located within the housing is a flash chamber with a needle extending from the distal end of the chamber and beyond the distal end of the housing. A tubular needle guard is located for distal movement within the semi-tubular needle housing, and has a distal opening through which the needle extends. The bottom of the needle guard is slotted to fit around the base of the flash chamber. At the rear of the needle guard slot is a portion of a locking mechanism which will engage with and lock in the needle housing when the needle guard is extended to cover the needle.
When an I.V. catheter is inserted into the patient, the user must have an indicator of some sort to signal successful entry of the introducer needle into the vein. The indicator is known as flashback and takes place in the flash chamber. Upon successful entry, the blood must travel through the length of the hollow needle and into a clear or translucent chamber opposite the penetrating end of the needle. The appearance of blood in this chamber is the flashback, and the chamber itself is the flash chamber. Once blood appears in the flash chamber, the user stops advancing the needle, and begins the process of threading the catheter tube into the vein.
It is important that the user see the flashback immediately otherwise there is a risk of continuing the needle advancement through the other side of the vein, without knowing that at one time they were already in it.
In most cases, a flash chamber with a large volume is best. One of the advantages of a large chamber is that it takes a period of time to fill the chamber, giving the user the opportunity to verify the continuation of blood flow. This ensures they are still inside, and have not penetrated through the opposite side of the vein.
In the small veins, when using the small needles, quick flashback and quick reaction speed are more important than when in larger veins. This is not only because the smaller veins are more fragile, but also there is less distance for the needle to travel before passing through the vein.
Unfortunately, the flashback is most difficult to see when using these small needle sizes with the typical large flash chamber design used today.
When dealing with very small needle sizes, the flashback can sometimes be no more than a small drop of blood. When only a small drop of blood presents itself, it can be difficult to see in the large flash chamber. In this situation, there is greater risk that the user will not see the blood becoming visible and react quickly enough to stop advancing the needle in time.
If the flash chamber were much smaller in diameter, the blood would be more visible in the cases of small flashback volumes. Yet, doing so would make the flash chamber unsuitable for use with higher volume flashback. Because the rate of flashback is unpredictable, and higher flashback volumes are more common than low flashback volumes, it would hinder more usages than it would help.